1. Field of the Invention
The present invention relates to a hydrophobic cationic dye suitable for image formation by sublimation thermal transfer recording and a thermal transfer ink ribbon using the same.
2. Description of the Prior Art
Hitherto, sublimation thermal transfer recording has been carried out to obtain high gradation full color hard copies from image information such as video or computer graphics. In the sublimation thermal transfer recording, the image recording has been performed by using a thermal transfer ink ribbon in which an ink layer having a sublimation dye or thermal diffusion dye dispersed in a hydrophobic polymer binder is formed on a polyester substrate, and a photographic paper in which a dye receiving layer comprising a hydrophobic polymer is formed on a synthetic paper substrate. More specifically, the ink layer of the ink ribbon is superimposed on the dye receiving layer of the photographic paper, and heat is applied on the polyester substrate of the ink ribbon by a thermal head or the like in accordance with an image signal, whereby migrating the dye in the ink layer to the dye receiving layer of the photographic paper to form an image.
As the dye used in thermal transfer ink ribbons for such sublimation thermal transfer recording, disperse dyes have generally been used taking the dispersibility in the hydrophobic polymer binder in the ink layer; however, it has recently been proposed to employ hydrophobic cationic dyes having more excellent sensitivity in the transfer, hue of images and light resistance than the disperse dyes (Japanese Patent Application Laying-open No. 6-40172). In the patent application, it has been proposed to use diazacarbocyanine hydrophobic cationic dyes for yellow color, oxazine hydrophobic cationic dyes for cyan color, and hemicyanine hydrophobic cationic dyes for magenta color (Japanese Patent Application Laying-open No. 6-40172).
However, the hemicyanine hydrophobic cationic dyes for magenta color have a problem of insufficient light resistance and transfer concentration. An attempt has been done to use a laurylsulfate salt of C.I. Basic Red 22 represented by the formula (2):
which is one of diazahemicyanine hydrophobic cationic dyes having more excellent properties such as light resistance and transfer concentration than hemicyanine hydrophobic cationic dyes, as a dye for magenta color.